Police said they arrested 38 people at Madison Square Garden on Saturday night during the first of four concerts by the hippie rock band Phish, with 36 of the collars for drug possession.

Two busts were for scalping or holding forged concert tickets.

With two nights played and two to go — including the band’s New Year’s Eve finale — there was no official word if cops also spent Sunday picking off “Phans.” Arrest figures for Sunday were not immediately available, a law enforcement source told the Post on Monday.

Concertgoers said the heat was still on. “I saw two people get bagged by undercovers in 10 minutes. They were out for blood tonight,” wrote one fan, “Dishphead,” on Sunday night on a Phish.net fan forum titled “security at msg.”

Others boasted of sneaking contraband past security.

“I stuffed a bottle of Jager in my waist band last night,” a fan named “SpreadheadJON” wrote on the forum. “Used some distraction methods. Shots for all!”

The Vermont-based band — known for its die-hard followers and its meandering, epic-length live shows — also draws great interest from law enforcement agencies.

Three shows during Halloween weekend at Atlantic City’s Boardwalk Hall netted 42 arrests – most for drug possession or distribution. Another 80 people were busted this summer during three days of Phish concerts in Saratoga Springs, and one 40-year-old concertgoer at the upstate gigs died of an overdose.